Known structures include a structure where a video display serving as a display means is openably and closably attached on a ceiling of a vehicle (for example, see Patent Document 1). Such a conventional technology uses a supporting structure where a rectangular display is connected to a housing through a hinge, and is supported rotatably about a fixed fulcrum. When the display is stored, it is maintained in the closed state where the screen thereof is placed alongside the ceiling, and when the display is used, it is maintained in a so-called opened state where the screen is displaced nearly to a substantially vertical state such that a viewer can easily see the screen. In such a viewable state, since the display occupies a space corresponding to the substantially longitudinal size of the display downwardly from its fixed fulcrum, driver's rearward visibility through a room mirror is blocked in the case where a large-sized display is used, or in a sporty vehicle with a low ceiling and sunroof-specification vehicle.
Further, in an on-vehicle AV device mounted on a ceiling part of a vehicle and having a function capable of tilting its monitor unit, there has been known a supporting mechanism of an on-vehicle AV device, including a drive means having a tilt drive mechanism for tilting its monitor; a position-detecting switch detecting whether or not the monitor is located at the stored position; and a control means controlling the drive means on the basis of a signal from the position-detecting switch (for example, see Patent Document 2).
In the aforementioned technologies, there is no disclosure indicating that the rotating shaft of the monitor is displaced. Furthermore, the technology discloses only a structure for detecting the stored position of the monitor (that is, when the monitor is located in the closed state); however, the technology does not disclose that, for example, with an apparatus having a function causing the monitor to displace the rotating shaft while making an opening movement, any opening angle of the monitor is detected. For this reason, for instance, when the monitor is opened wider than a viewable angle and the display comes into the sight of a driver, no safety measures such as turning off of the display of the monitor can be taken. Even if an arrangement is adopted such that the monitor is locked against a further rotating movement so as to be unable to open wider than a predetermined viewable angle, it still remains that the shock given to a person coming in contact with the monitor cannot be reduced.    Patent Document 1: JP-A2002-193045    Patent Document 2: JP-A2002-204409
In conventional on-vehicle display units, the rearward visibility of a driver through a room mirror is sometimes blocked as the display size increases or due to other reasons. Moreover, if the display is opened wider than a viewable angle by some reasons and therefore, the display comes within the sight of the driver, safety measures cannot be taken such as automatically turning off the display because there is no detecting means for detecting that the display is opened wider than the viewable angle.
The present invention has been made to solve the above-mentioned problems. An object of the present invention is to provide a display opening and closing angle detecting mechanism capable of reducing a disincentive acting on a driver to concentrating attention during driving, accompanied by installation of a display.